Motor control system



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AC. SUPPLY INVENTORS ERNEST G. ANGER Donn L. PETT\T BY 7 ATTORNEY UnitedStates Patent 3,056,670 MOTOR CONTROL SYSTEM Ernest G. Anger and Dam L.Pettit, Wauwatosa, Wis, assignors to Square D Company, Detroit, Mich, acorporation of Michigan Original application May 9, 1955, Ser. No.507,083, now Patent No. 2,885,616, dated May 5, 1959. Divided and thisapplication Sept. 23, 1958, Ser. No. 762,770

6 Claims. (Cl. 318-72) This invention concerns a novel electricalcontrol system providing for the regulation of speed of two or moredirect current motors, which operate a continuous conveyer belt line forthe processing of various types of materials, such as, for example,plasterboard or wallboard and is a division of our application 507,083,filed May 9, 1955, now Patent 2,885,616.

It is an object of this invention to provide an adjustable controlsystem for regulating a motor driven process line which incorporatesspeed regulation of a main generator by control of the excitationsupplied thereto to operate the line at a preset speed, and in additionprovides adjustable position control between sections of the line toaccomplish section speed regulation under varying load conditionsconcurrently with line speed regulation.

A further object of the invention is to provide a control system formaintaining proper speed relationships between different sections of acontinuous process line to compensate for motor speed and processmaterial changes occurring along the line.

A still further object of the invention is to provide a method ofsynchronizing a shearing motor in the process line to the motion of thematerial by means of an electrical signal transmitted by a meteringwheel driven by said line, with provision for introduction of anadjustable correcting slip to permit small corrections in the speedrelationship.

A still further object of the invention is to provide an adjustablemeans to effect a speed percentage change between two section drivemotors to compensate for different section requirements.

It is a still further object of the invention to provide for theregulation of two or more motors to exact coordination, or whennecessary an adjustable speed difference, by continuously comparingtheir relative angular positions, obtained by comparisonself-synchronizing devices cooperating with a motor field weakeningpotentiometer in a novel arrangement.

It is a still further object of the invention to provide for theregulation of a motor, as above, except instead of regulating throughcomparison self-synchronizing devices and a field weakeningpotentiometer, regulation is obtained through comparisonself-synchronizing devices and a magnetic amplifier circuit.

It is a still further object of the invention to provide a motor speedcontrol system in which the field windings of the motors are connectedin series circuit relationship to minimize speed differences and theeffect of temperature variations between the motors.

It is a still further object of the invention to provide for theregulation of position of one direct current motor by comparison of theangular position of said motor with the angular position of anotherdirect current motor, or the angular position of a metering wheel in theprocess line.

These and further objects and features of the invention will be readilyapparent to those skilled in the art from the following specificationand appended drawings illustrating certain preferred embodiments inwhich:

FIG. 1 represents a block diagram of a plasterboard conveyor beltprocess line.

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FIG. 2 represents a schematic wiring diagram of the main drive regulatorportion of the control system.

FIG. 3 represents a combined block and schematic wiring diagram of thetwo representative belt sections of the control system.

FIG. 4 represents a combined block and schematic wiring diagram of tworepresentative belt sections of the control system, similar to FIG. 3,but illustrating an'added feature for effecting an adjustable speeddifference between the respective sections.

FIG. 5 represents a schematic wiring diagram of the start and stopportions of the control system.

FIGS. 6, 7, 8, and 9 represent combined block and schematic wiringdiagrams of two representative sections of the control system withalternative methods of regulation.

This invention will be described in connection with a wallboard orplasterboard process line manufacturing system merely as arepresentative embodiment thereof. As illustrated in FIG. 1, the rawmaterial for plasterboard manufacture is fed into a hopper and .theninto a mixer, where it is mixed with water to proper consistency in amixing head and fed out onto a lower roll of paper. It then feedsthrough the forming rolls where the lower roll of paper is folded up andover the edges and the upper layer of paper is placed on top. As itpasses through the forming rolls, the paper and mudlike materialcombination is reduced to the required thickness and glue is applied tothe edge of the paper to secure the upper and lower parts together. Itthen feeds out onto the first belt section at a rate of speed which isadjustable on the machine, from 30 to 100 ft. per minute, for example. Aplastic tape is fed under either side of the soft board to reduce theedge thickness so that in the construction of the home a piece of tapecan be placed over the adjacent matching boards without being noticed.This plastic tape proceeds along the first two belt sections until theboard begins to set. As the board passes along the first belt section,it is rather soft and pliable and does not set up to any degree ofhardness until it is on the second belt section. On the third beltsection it is somewhat harder and passes into the live roll sectionwhere it is exposed to air for drying of the underside. From here itpasses into the punch and knife section.

The punch section is used to punch the holes in plasterboard only and isdisengaged for the wallboard process. This punch punches the holeswithout interrupting the movement of the board. It is driven withelliptical gears so that the punch may enter the board and leave theboard while the punch head is moving along the line at the same rate asthe board.

The knife section consists of a lower knife 77 (FIGS.-

6, 7, 8, and 9) With blades at positions rotating in synchronism withthe board. An upper knife 78 (FIGS. 6, 7, 8, and 9), consisting of asingle blade, is arranged with a clutch and triggering mechanism to bebrought into action by a chain and dog release (not shown), to cut theboard to any desired length in multiples of 1 ft. from 4 ft. to 16 ft.,for example. The board then passes on to an accelerating section and isfed out onto a reversing table, where it changes direction to feedthrough an 3 armatures 4G, 50, 60, 70, 80 and 90 through points AA(FIGS. 2, 3, 4, 6, 7, 8, and 9). Note that these direct current drivemotors 4t), 50, 6t), 70, 80 and 9t and their corresponding armaturesbear the same numbers, as they are functionally identical for purposesof this description.

The main drive regulator circuit has an alternating current power supplywhich furnishes a relatively constant voltage through a constant voltagetransformer 37 to a rectifier bridge 35. The bridge 35 supplies arelatively stable direct current voltage across the potentiometers 38and 36 to provide a reference voltage for the main regulator circuit.

Contacts 19, controlled by relay 17 (FIG. connect the alternatingcurrent power supply with a dry disc rectifier stack 21, which furnishesa direct current excitation voltage to the generator field winding 23.The rectifier stack 21 forms part of a magnetic amplifier circuit to besubsequently described. The rectifiers of stack 2-1 are connected in abridge-arrangement with output windings 26 and 28 of a magneticamplifier reactor unit 25 included in two legs of the stack 21. Controlof the saturation of the iron in the core of reactor unit 25 providescon trol of the circuit and the DC. voltage applied to the generatorfield 23 in a manner well known in the art.

A second saturable reactor and its corresponding rectifier stack 22 forma second magnetic amplifier circuit which is connected in cascade, asthe first stage, with the magnetic amplifier circuit of reactor andstack 21 as the second stage. The direct current control winding 13 ofreactor 15 is connected between a pair of potentiometers 38 and 39. Thepotentiometer 38 is connected to potentiometer 36 across the rectifiedoutput of rectifier and permits a line speed adjustment of the referencevoltage to be obtained. The potentiometer 36, in series withpotentiometer 38, permits an adjustment for minimum speed. Thepotentiometer 39 connected in series with a resistor 53 and across theoutput of tachometer generator 52, permits an adjustment of the maximumspeed in a manner to be subsequently described. A

potentiometer 34, in series circuit with the control Wind- A ing 13, hasa slider 47 permitting adjustment of a damping signal voltage in amanner to be subsequently described.

The tachometer generator 52, electrically connected across potentiometer39 and resistor 53, is mechanically coupled to the first belt motor andfurnishes an electrical output in direct proportion to the speed of saidmotor. It is not necessary that tachometer generator 52 be mechanicallycoupled to the first belt motor 40 but may be connected to any of thebelt motors because its response is to be indicative of the actual speedof the line.

Referring now to :FIG. 3, in which is shown, for example, the first twobelt sections of the process line, the field winding 40A of motor 40 isconnected in series with the field winding A of motor 50 and connectedat points D and B to the direct current output of rectifier 30 (FIG. 5).In order to regulate one belt speed with respect to the next, all beltmotor field windings 40A, 50A, and the field windings (not shown) ofmotors and 90 are placed in series with bridging resistors across eachfield to obtain speed control by field weakening. For example, only thefield windings 40A and 50A are shown, because the other field windingsare connected in the same manner. The adjustable bridging resistors 61and 62 are connected in shunt circuit with the field windings to provideadjustable field weakening in conjunction with potentiometer 46 inamanner to be subsequently described.

The angular position of each motor armature, as well as the speedrelationship of one section compared to the next, is controlled by theuse of a differential control system which indicates the position andreflects the position and speed discrepancy between adjacent motors tovary the resistance in the field shunting circuits. In the followingdescription and in the claims, reference is made to synchro transmittersand receivers. These are selfsynchronizing devices commonly known asSelsyns or synchros which are well known in the art. They may beconnected either as transmitters (generators) to translate a mechanicalindication reflecting a motor position into an electrical output, or asa receiver (motor) to translate an electrical indication into amechanical output to change a position. A synchro transmitter 41,mechanically coupled to and driven by belt motor 40 to obtain anelectrical voltage output indicative of the speed of said motor, iselectrically connected to an AC. supply source and has its electricaloutput connected to one side of a differential syncho receiver 44. Asecond synchro transmitter 42, mechanically coupled to and driven bybelt motor 50, is electrically connected to the same alternating currentsupply source and has its electrical output connected to the other sideof differential syncho receiver 44. The differential synchro receiver44, operated in a reverse sense from the synchro transmitters 41 and 42,is connected in series circuit therewith and has for the utilization ofits mechanical output a direct connection with a potentiometer 46. Onearm of the potentiometer 46 is connected in the circuit of resistor 61which shunts its associated motor field winding 40A while the other armof the potentiometer 46 is in the shunting circuit of the succeedingsection (resistor 62) of motor field winding 50A.

An alternate system is shown in FIG. 4 wherein a differential synchrotransmitter is inserted in series circuit with the differential synchroreceiver 44 and synchro transmitter 41 and is mechanically coupled toand driven by an adjustable means 45. The adjustable means 45 is anadjustable transmission device which is driven by a motor and in turndrives another device at any preselected speed difference. Theadjustable transmission 45 is mechanically coupled to and driven bymotor 40 and is adjusted to drive the synchro transmitter 43 at areduced speed.

Referring now to FIG. 6 in which is shown the live roll section, itsmotor 7t) and the punch and knife section and its motor 80. A synchrotransmitter 79 is mechanically coupled to and driven by a metering Wheel75 which is provided to meter quantities of the prepared plasterboardinto position for the subsequent punch and shearing operation. Thesynchro transmitter 79 is electrically connected across a source ofalternating current supply and has its output electrically connected tocomparison transformers 87. A synchro transmitter 81 is mechanicallycoupled to and driven by the punch and knife motor and electricallyconnected across an alternating current supply and has its electricaloutput connected to a differential synchro transmitter 85. Thedifferential synchro transmitter has an adjustable transmission means 83mechanically coupled to and driven by the knife motor 80. The adjustabletransmission means 83 operates in a manner similar to the adjustabletransmission means 45 to introduce a speed difference signal to thecomparison circuit consisting of synchros 79, 81, 85 and transformersS7. The output of transformers 87 is connected to a magnetic amplifiercircuit consisting of rectifier stack 89, saturable reactor 93 andrectifiers 94. A rectifier 92 connected across an alternating currentpower supply supplies a direct current excitation voltage to the fieldwinding 80A of motor 89. An adjustable resistor 95 in the control signalcircuit permits adjustment of the maximum signal current and, therefore,of the maximum current of field winding 80A, and thereby adjustment ofthe minimum speed of motors 80. An adjustable resistor 97 in series withthe field rectifier 92 permits setting of the maximum field and,therefore, maximum speed of motor 80.

In FIG. 7 is shown a system similar to the system of FIG. 6 with analternative method of regulation. In this system the synchro transmitter79 is mechanically coupled to and driven by the live roll motor 7 0instead of the metering wheel 75 of FIG. 6. The remaining components areidentical to and operate in the same manner as the correspondingcomponents of FIG. 6.

In FIG. 8, comparable to FIG. 7, and in FIG. 9, comparable to FIG. 6,the speed difference output of the synchros 79, 81 and 85 is connecteddirectly to the rectifier bridge 92 through an adjustable rheostat 82.The remaining components are identical to and operate in the same manneras the corresponding components of FIG. 6, heretofore described.

Referring now to FIG. 5 in which is shown an alternating current supplytransformer 14 which has its output connected to a rectifier bridge 30.The bridge 3% is connected at points B and D to supply direct currentpower to the field windings 40A, 50A, 60A, WM, and @fiA, as previouslymentioned. A start and stop circuit is shown connected across the outputof rectifier 3t and has a start relay 17 in series with the start andstop buttons. The relay 17 operates contacts 18, 19 and contactors 15.The latter two components are shown in their circuit relationships inFIG. 2.

Operation In operation, closure of the start button energizes the relay17 to close contacts 18 (which complete a holding circuit around thestart button), closes contactors l5 and closes contacts 19 (FIG. 2). Theclosure of the contacts 19 energizes the main drive regulator circuit,and the clossure of contactors 15 starts the operation of the motorgenerator set (lid2fi). The motor M) is regulated to a predeterminedspeed by variation of the excitation voltage applied to generator fieldwinding 23, and because the output of generator 2i) is connected inparallel with all the motor armatures 4t), 50, 6t 7t}, 8%, and 90, willthereby maintain approximate speed of all the drive motors. These speedsand relative positions of the motors are further regulated to exactsynchronization by regulators to be described below.

It will be observed that the series connection of fields minimizes theeifect of field resistance variations due to differences in temperaturebetween the respective motors. Some of these motors might operate nearovens or in open sunlight, whereas others are in a fairly cool portionof the building. With the motor fields in series, the warm-up of any onefield affects them all and thereby minimizes the eifect, thus reducingthe amount of regulating correction required by the control system. I

With a preset speed position of potentiometers as, 38 and 39 selected bythe operator and rectifier 35 providing a relatively stable referencevoltage at slider 38A, and prior to initial movement of motor 4%, arelatively large voltage is reflected across the control winding 13 ofsaturable reactor 15 and a resulting high current therethrough. Theout-put of the saturable reactor 15 is controlled by the direct currentdrawn through its control winding 13 and therefore with a high current,the output across the rectifier stack 22 is decreased and transmitted tothe control winding 31 of saturable reactor 25. The rectified output ofreactor 25 is applied across the field winding 23 of generator 26}. This-will initiate voltage increase of generator 20 when contact 19 closesin response to energization of its coil 17, and result in accelerationof the drive motors 40, 50, 6h, 70, 80, and 90. The initial accelerationof motor '40 will be transmitted back through the mechanical coupling tothe tachometer generator 52 where it is refiected in a feedback voltagesignal across potentiometer 39 and resistor 53. The feedback voltagesignal of tachometer generator '52 will oppose the reference voltageheretofore applied at potentiometer slider 38A and across the controlwinding 13.'

The adjustment of the maximum speed potentiometer 39 causes the feedbackvoltage at maximum operating speed to be slightly greater than thevoltage at potenti ometer 38. This small difference is sufiicient tomaintain the flow of regulating control current. A strong regulatingaction is then provided, since a small deviation of tachometer voltagecan cause a considerable change in control current (through winding 13)and magnetic amplifier output to accomplish a correcting change to thegenerator 20. Thus, when the preset speed of motor 40 is attained, thefeedback voltage at potentiometer slider 39A will match the referencevoltage at potentiometer slider 38A and will reflect its match acrossthe control winding 13. The match of voltages then maintains the speedof motor 40 and its follower motors to the preset speed position.

In the event the operator changes the preset speed to accelerate ordecelerate the process line, a damping effect is provided to preventsudden speed changes. A potentiometer 34, in series circuit with theWinding 13, has a slider 4'7 which permits adjustment of the dampingsignal voltage transmitted from rectifier 21 through capacitor 49, whichis of a polarity to momentarily oppose any change of voltage produced bychange of potentiometer. This may be further explained as follows: Asthe voltage applied to the field winding 23 increases, current drawn bythe damping capacitor 49 through filter choke causes a voltage dropacross the damping potentiometer 34 which strongly opposes the voltageapplied to the control winding 13 by the speed potentiometer 3b. Therate of voltage increase and therefore the response is limited until thecapacitor 49 is fully charged to thereby delay or dampen the speedchange until tachometer feedback at the new voltage again matches thereference voltage. The choke coil 48 produces filtering of rectifierripple components from this voltage. The effective new excitationvoltage will be fed through a dual magnetic amplifier circuit fortransmittal to the generator field winding 23 to provide amplifiedexcitation voltage to change the speeds of the belt motors ii? etc. Thesensitivity of the dual magnetic amplifier circuits permits full changeof output with a fraction of a volt applied at the control winding 13.

A bias control winding 27 of saturable reactor 25 is connected acrosspotentiometers 4 and 6. The potentiometer 4 is an adjustable biasresistor which is utilized to provide a bias for the saturable reactor25 in its control characteristic in the desaturation direction. Thepotentiometer 4 is adjusted so that minimum output to the field winding23 at correct required speed may be obtained with suficient current, ofsaturating polarity,

drawn through the control winding 31 to insure operation through afavorable range of the pro-amplifier (15 and 22) output characteristic.The bias current is not varied by change of the speed settingpotentiometer 38 and, since the magnetic amplifier output is determinedby the algebraic sum of all control ampere turns, this winding 27 merelyshifts the curve of output versus control.

Also included in the bias winding circuit is an adjustable IRcompensating potentiometer 6. This potentiometer 6 is connected acrossthe generator commutating field 33, so as to receive a voltage dropwhich is proportional to the current load drawn by the motors 40, 60,70, 8t} and 9t and is of a polarity to reduce the bias current as theload increases. It is adjusted so that the resulting shift in theamplifier output characteristic by the change in bias current causes anincrease in the amplifier output to the generator field 23 so as toraise the voltage applied to the motor armatures 40, 50, 60, 7t), 8t?and 9t enough to compensate for their resistance drop and armaturereaction eifect. This compensation reduces the required regulation ofthe magnetic amplifier circuit.

A control winding 29 of reactor 25 is connected in series with sectionsof a current limit rectifier 8 and a currentlirnit potentiometer 9. Thepotentiometer 9 is connected across the generator commutating field 33,similarly to potentiometer 6, and has a voltage drop proportional to thegenerator armature current. A biasing current drawn through resistor 7from the reference voltage supply causes a constant voltage drop to bemaintained across the left section of rectifier 8. The polarities ofthis voltage are such as to prevent conduction through the remainingsections to the winding 27, connected at their junction. Filter choke 5and capacitor 3 prevent rectification of harmonic voltages present inthe winding 27. When accelerating or steady load condi tions increasebeyond the limit set by the slider of potentiometer 9, the bias voltageis exceeded and current is conducted through the single disc section ofrectifier 8 to the resistor 7. This current flows through the Winding 29in a direction to decrease the saturation of the magnetic amplifier(ZS-2T), and is strong enough to overcome the regulating action of thecontrol. Winding 31, since the resistance in the current limit circuitis low. The generator field 23 is prevented from increasing too rapidly,or weakened, if necessary, so as to limit the current flow from thegenerator to the motor armatures until the motors 40, t), 6t], 70, 80,and $3 accelerate. When the speed increases to the preset value, thefeedback of tachometer voltage permits the regulating windings 31 and13, as heretofore mentioned, to resume control, and the generatorarmature current decreases to the amount required by the running load.

If the speed setting is decreased suddenly, decelerating current flowsas voltage generated by the motors 40, 5%, 6t 7t 8t and 90 exceeds thatof the generator 20, and the voltage across potentiometer 9 reverses.The other section of rectifier 8 then conducts current through theWinding 29 in the opposite or saturating direction, as soon as thethreshold conduction potential is exceeded. The bias section ofrectifier 8 is then by-passed. This saturating current through winding29 prevents weakening of the field 23 too rapidly so that thedecelerating current is limited to a low value until the new presetspeed is attained.

The operation of the system for differential angular position and speedcontrol will now be described, as illustrated in FIGS. 3, 4, 6, 7, 8,and 9. The differential speed regulating system is provided to hold therelative angular position relationship between the three belt sectionmotors 40, 50, and 60 and the live roll motor 70 in closesynchronization for any selected line speed. The system also permitsindependent adjustment of the slip between successive sections to insurethat proper tension is maintained at every portion of the wetplasterboard as it' travels from the forming rolls to the roll table. InFIGS. 3 and 4, with the process line in operation, a motor speeddifference between motors 40 and 50, occasioned by changing loadcharacteristics of the plasterboard material, necessitates individualmotor speed correction to maintain smooth and continuous operation ofthe process line. In this event the angular position of each motorarmature is compared by its corresponding synchro transmitter. Becausethe synchro transmitters 41 and 42 are directly coupled to and driven bytheir corresponding motors 40 and 50, any angular displacement betweenthe motors 40 and will result in a corresponding angular displacementbetween the rotors of synchro transmitters 41 and 42. Also, because thedifferential synchro receiver 44 is connected in series with thetransmitters 41 and 42, any change in their angular displacement will becommunicated as a voltage to the receiver 44, with polarity according tothe transmitter having the greater speed. The synchro receiver 44 willthen rotate to move the potentiometer 46 a small distance to provide thecorrective field weakening necessary to bring the motors 40 and 50 intosynchronization. Obviously, if no angular displacement exists betweenthe motors 40 and 50, indicating proper speed relationships, no voltagewill be present at receiver 44 and it will be at rest until an unbalanceis indicated and it again moves to correct the unbalance.

In some instances it may be desired to slightly increase or decrease thespeed of one motor in relation to the next by introducing a setpercentage of slip to accommodate, for example, difference in the beltdrive pulleys and shrinkage or expansion of the plasterboard. This maybe obtained (FIG. 4) by the use of the adjustable transmission means 45and a differential synchro transmitter 43 to introduce a speedcorrection difference. The operator, after determining that one motor isleading or lagging its adjacent motors, makes an initial manualadjustment on the adjustable transmission 45 which introduces amechanical speed difference to the differential transmitter To comparewith the speed of synchro transmitter 41, the synchro transmitter '42must then run at a speed which equals the speed of motor 46 plus thedifferential introduced by the speed difference synchro transmitter 43.If this condition is not maintained, the difference synchro transmitter43 will rotate and introduce a correction signal through itsdifferential synchro receiver 44 and thereby to the potentiometer 46,which will correct the speeds of the two motors until the difierencesynchro transmitter 43 comes to rest, whereupon the speed of motor 50will equal that of motor 40 plus the speed difference fed in. Note thatin FIG. 3 the position difference between the synchros 41 and 42 isdirectly connected by the synchro receiver 44 to the potentiometer 46 toprovide a synchronous position correction system, without providing fora speed difference system as shown in FIG. 4. Resistors 6t and 62 oneither side of the synchro driven potentiometer 46 permit adjustment tolimit the field control range as well as center the normal operatingposition of the potentiometer 46. This adjustable setting, by providingan operating range, prevents excessive weakening of the field Which itshunts to prevent any dangerous rise in motor speed.

Note that the position difference control of this system obtains thebest possible results because initially the plasterboard is so soft thattension between belts 1 and 2 must be held so low as to cause aregulating problem and there is considerable change in the length of theboard as it progresses through its curing cycle so that the board isalways swelling or shrinking as it proceeds along the belt line. Thesepositions of swelling or shrinking are not stable points along the line,but vary with the speed of the line and quality of the mix being used.Other conditions, such as temperature and humidity, also affect thiscuring cycle. Therefore, these considerations require the use of motorposition difference control to obtain proper regulation of the processline. Of particular importance in observing this system is that theregulated difference in speed of the belt sections is a preset smallproportion of the overall line speed, for example, the adjustable ratiotransmission 45 of FIG. 4 has an accuracy of a small fraction of 1% ofits maximum setting and is geared to provide a 3% maximum correction atthat setting. The maximum differential error therefore that theregulator can permit is less than .03%. Since the synchros are drivenwith sprocket gears (not shown), no further inaccuracy would beintroduced because of slip.

One of the objects of the invention was to provide precise shearing orcutting of the board lengths. This object is obtained by providing ametering wheel (FIGS. 6 and 9) which meters the quantity of board comingoff the live rolls 76 into position near the rotary knives 77 and 73.The knife motor armature is powered from the same voltage (generator 20)as the preceding and succeeding motors, and therefore tends to runapproximately in proper speed relationship with the other drive motorsfor all speed settings. To provide close control of the cutting orshearing operation, faster regulation of the knife sectron is required.This is obtained by a rapidly acting position regulating system, whichholds the speed of knife motor 80 in exact synchronization with theplasterboard line speed by set adjustment of its speed through controlof field MA. A magnetic amplifier circuit'in FIGS. 6 and 7 improves thespeed of regulation by providing a field forcing effect. In FIG. 6, themetering wheel 75 controls the field winding 80A through the magneticamplifier by its coupled synchro transmitter 79 which gives a directmeasurement of the movement of the board. This system is similar to thebelt motor regulators heretofore described, in that position synchrotransmitters 79 and 811 are employed in connection with the meteringWheel 75 and the knife motor 80 respectively, with a 9 speed differencebeing fed in by an adjustable transmission 83 to a synchro transmitter85. However, a different method is employed to regulate the fieldwinding. A voltage output from the synchro 79, reflecting the relativeposition of metering wheel 75, is compared with the voltage output ofsynchro 81, reflecting the relative position of knife motor 80, modifiedby the small diiference voltage of the speed difference synchro 85 whichreflects the speed difference required. The voltage difference in theelectrical signals transmitted to the synchro combination til-85 drivenby the motor 80 and the synchro 79 driven by either the metering wheel75 (FIG. 6) or the motor 70 (FIG. 7) is compared by three transformers87 connected between synchros 79 and 85. The output of thesetransformers 87 is combined and rectified through rectifier stack 89 toprovide a direct current signal through the control winding 91 of themagnetic amplifier system. This current is approximately proportionalover the range of regulation to the instantaneous difference in angularpositions of the synchros 79 and 81 plus the adjustable speed differenceprovided by transmitter 85. To provide the maximum possible speed ofresponse, which requires overcoming the highly inductive field winding80A, direct feedback of the currentof field winding 80A is employed.This is accomplished by connecting the control winding 91 so as toreceive a current which is the difference between the control signaloutput and the current of field 80A, both of which are several timesthat required to change the conduction of the saturable reactor 93. Themagnetic amplifier circuit and its saturable reactor 98 thenautomatically is required to regulate its output current through thefield 80A at a value slightly greater than the signal current, bytheamount required by the control for that output. When the minimum andmaximum field adjustment resistors 95 and 97 are properly adjusted, therectified signal is strong enough to overcome the field currentfeedback. It is then able to exert considerable forcing action toaccomplish a change in the field current quickly, since a smalldiscrepancy in the difference between the signal and feedback currentsis able to swing the amplifier saturation completely to either end ofits range temporarily until the required change of current isaccomplished. With this system, the speed of knife motor '80 can bechanged rapidly with respect to the line speed by small and accurateamounts through use of the adjustment on the speed dififerencetransmission. In

this way the length of board passing through the knife between cuts canbe controlled accurately.

I11 FIG. 7 the same system is used, except that the position signal fromthe acceleration belt motor 70 is communicated to the synchro 79 insteadof the signal from the metering wheel 75 which may be omitted. Thissystem then regulates the motors 70 and '80 to maintain synchronizationbetween the two sections.

In FIG. 8, comparable to FIG. 7, and FIG. 9, comparable to FIG. 6, theposition difference signal is fed directly to a rectifier bridge fortransmittal to the knife motor 80A without amplification as a moreeconomical method of modification but without field forcing action. Inall other respects the components of the systems of FIGS. 7, '8, and 9are identical in kind and operation to the components of the system of'FIG. 6 heretofore described.

In the following claims, reference is made to position responsive meansand differential means which are contemplated to include mechanicalequivalents for the synchro transmitters (position responsive means) andthe difierential synchro receivers (differential means). Obviously,where location distances are not a factor, a mechanical coupling, suchas a flexible shaft, may be inserted between the motor 40 and adifferential transrnission device, such as differential gears, and asecond flexible shaft connecting motor 50 and the same transmissiondevice to produce a mechanical output driving the potentiometer 46 inproportion to the angular position or speed variation existing betweenthe motors. In essence, such a mechanical system would be very practicalwhere the belt motors 40 and 50 are located within short distance ofeach other. In the particular application disclosed in this invention,distances between motors 40 and 50 of several hundred feet are requiredwhich necessitates electrical coupling as a more pracical method ofapplication.

Therefore, while certain preferred embodiments of the invention havebeen disclosed, it is understood that the invention is not limitedthereto, as many variations will be readily apparent to those skilled inthe art and the invention is to be given its broadest possibleinterpretation within the terms of the following claims.

What is claimed is:

1. In a motor regulating system, a plurality of direct current motors, afirst direct current source for supplying power to the armatures of saidmotors, said armatures connected in parallel circuit with each other andsaid source, a second source of direct current supply, field windingsfor said motors connected in series circuit with each other and saidsecond source, a synchro transmitter for each motor and mechanicallycoupled thereto to provide an electrical response representative of theangular position of said motor, variable resistance means in shuntcircuit with at least one of said field windings to vary the resistancethereof, a synchro receiver in series circuit between two of saidsynchro transmitters 'to receive and compare their electrical outputsand to provide an output representative of the difference therebetween,said synchro receiver mechanically coupled to said resistance means tovary the current through said field windings in relation to said outputdifference.

2. In a motor regulating system, a pair of direct current motors, adirect current source connected to the armatures of said motors, fieldwindings for each of said motors, said field windings being connected inseries with each other, a position responsive means for each motormechanically coupled thereto to provide an output representative of theangular position of its motor, a variable reistance means in shuntcircuit with at least one of said field windings to vary the resistancethereof, a differential means interposed between two of said positionresponsive means to receive and compare their respective outputs, anadjustment means mechanically coupled to one of said motors and saiddifferential means to furnish an adjustable relative difference betweenoutputs of said two position responsive means, said diiferential meansmechanically coupled at its output to said resistance means to vary therelative current through said field windings to maintain said motors atthe adjustable speed difference.

3. In a motor regulating system, a first direct motor, a second directcurrent motor, a motor-generator set driving said motors at apredetermined speed, a first field winding for said first motor, asecond field winding for said second motor, a source of direct currentsupply providing a constant excitation voltage for said field windings,said field windings connected in series circuit to said source, variableresistance means connected in shunt circuit with said field windings andhaving a connection to a point between said field windings, a firstposition responsive means associated with said first motor, a secondposition responsive means associated with said second motor, said firstand second position responsive means connected to a differential meansto provide a comparison output when one of said motors varies from saidpredetermined speed as reflected by a corresponding angular positionvariation, means movable in response to said comparison output to movesaid variable resistance means in accordance therewith to change theshunting resistance in the circuits to said field windings whereby saidmotors are maintained in speed synchronization with each other at saidpredetermined speed.

4. In a motor regulating system, a plurality of direct current motors, amotor-generator set providing electrical power to the armatures of saidmotors, a source of direct current supply, field windings for saidmotors connected in series circuit with each other and said source, aposition responsive means connected to each of said motors to provide anoutput representative of the position of said motor, a variable resistorin shunt circuit with at least one of said motor field windings to varythe current therethrough, difierential means connected to two of saidposition responsive means to furnish an output difference, saiddifierential means being mechanically coupled to said resistor to varythe resistance thereof in relation to the relative position of themotors affecting said two position responsive means.

5. In a motor regulating system, the combination comprising, a pluralityof direct current motors each having a field winding connected in aseries circuit with the field windings of the other motors, transmittingmeans mechanically coupled to at least two of the motors to provide anelectrical output representative of the angular position thereof, avariable resistance in shunt circuit with the field winding of at leastone of the two motors to vary the resistance of the field winding, areceiver in electrical circuit with the transmitting means of the twomotors to receive and compare their electrical outputs and to provide anoutput representative of the difierence therebetween, and a connectionbetween the receiver and said resistance to vary the resistance inrelation to the output of the receiver.

6. In a motor regulating system, a pair of direct current motors to beregulated at a predetermined speed difference, a source connected tosupply the armatures of the motors with current, field windings for eachof the motors connected in a series circuit with each other and a secondcurrent source, a position responsive means for each motor mechanicallycoupled thereto to provide an output representative of the angularposition of the motor connected therewith, means for varying therelative impedance of the field windings of the motors, an adjustmentmeans mechanically coupled to one of the pair of motors and connected toreceive and adjust the output of the position responsive means connectedwith the said one of the pair of motors and to provide an outputadjustably difierent than the output of the position responsive meansconnected therewith and a differential means interposed between theadjustable means andthe position responsive means connected with theother of said pair of motors to receive and compare their respectiveoutputs and provide an output representative of the differencetherebetween, said differential means being mechanically coupled to themeans for adjusting the relative resistance of the field windings tovary the current through the field windings to maintain said motors atan adjusted speed ditference.

References Cited in the file of this patent UNITED STATES PATENTS2,451,946 Harris Oct. 19, 1948 2,735,059 Schaelchlin Feb. 14, 19562,799,817 Matthes et al July 16, 1957 2,858,493 Hull et al Oct. 28, 19582,882,474 Bessire Apr. 14, 1959 FOREIGN PATENTS 853,962 France Dec. 23,1939

